This textbook details the fundamental equations that describe the fate and transport of contaminants in the environment and covers the application of these equations to engineering design and environmental impact analysis relating to contaminant discharges into rivers, lakes, wetlands, ground water, and oceans. The second edition updates and improves the content of the first edition and new topics on nutrient and pathogen models in streams, and more coverage of calculating total maximum daily loads (TMDLs.) There are several distinguishing features of this textbook, such as: detailed coverage of the science behind water-quality regulations, state-of-the-art methods for calculating TMDLs for the remediation of impaired waters, modeling and control of nutrient levels in lakes and reservoirs, design of constructed treatment wetlands, design of aquifer (ground water) remediation systems, design of ocean outfalls, and the design systems to control the quality of surface runoff from watersheds into their receiving waters. The book includes numerous real-life practical examples, end of chapter problems, and a solutions manual containing the solutions to all end-of-chapter problems.